The casting of molten metal in sand molds conventionally involves the steps of compacting sand in a flask, around a pattern, then removing the pattern to form a mold cavity within which molten metal is cast and solidified. The flask comprises an upper, cope frame and a lower, drag frame which are aligned, one above the other, with the pattern arranged between and within them. Sand is packed into the frames, around the pattern, to form cope and drag mold sections Then, these sections are separated, the pattern is removed, and the sections placed together to provide the mold cavity therebetween.
In production type foundries in which numerous identical castings are made, it is common to form the sand casting molds within mold making machines. In using such machines, a match plate having pattern halves on each of its faces is positioned beneath the open bottom of a drag frame and sand is dumped into the open top of the frame. Then the drag frame is inverted so that the match plate is on the now upper, inner end of the drag frame.
Next, a cope frame is positioned, in alignment, upon the drag frame and match plate and sand is dumped into the open, upper end of the cope frame. Then, squeeze plates, which are plates positioned upon the open upper, end of the cope and the open, lower end of the drag, are pressed towards each other to compact the sand within each of the frames towards the match plate and the pattern.
After the sand is suitably compacted within the cope and drag frames, the two frames are separated and the match plate, with the pattern, is removed. After that, the cope and drag frames, filled with the compacted sand fillings, are realigned to provide the closed cavity, from which the pattern had been removed, within which molten metal may be cast.
The density or compactness of the sand filling within the sand mold depends upon the amount of force applied to the squeeze plates and the degree of movement of the plates towards each other for squeezing the cope and drag fillings between them. Because the production of sand molds within a sand mold machine is automated, and the molds are very rapidly produced, as for example, four to five molds per minute, it has not been feasible to vary the degree of compacting of the sand filling within a mold. That is, a substantially uniform, sand density or compactness is obtained by the machine formation of sand molds. But, in many sand casting operations, it is desirable to vary the amount of compactness or density of the sand mold within different parts of the mold. For example, it may be desirable to have a harder, more dense area at different parts of the pattern for better and more effective casting purposes. This has not been feasible with available sand mold making machines.
There has been a need for a means for providing different density areas within sand casting molds that are formed by mold making machines. Thus, this invention relates to an improved squeeze plate construction and method of operation by which the density and, consequently, the hardness, of the compacted sand within a sand casting mold may be varied, as desired.